F#的标准类型事件是什么

Question

我正在尝试从F#订阅/取消订阅C#(在RabbitMQ客户端库中(：

AsyncEventingBasicConsumer.cs

public event AsyncEventHandler<BasicDeliverEventArgs> Received;

AsyncEventHandler.cs

public delegate Task AsyncEventHandler<in TEvent>(object sender, TEvent @event) where TEvent : EventArgs;

我通过以下操作订阅了该事件：

let subscribeAsync (channel: IModel) exchange callback =
let consumer = AsyncEventingBasicConsumer(channel)
consumer.add_Received(AsyncEventHandler<BasicDeliverEventArgs>(fun sender args -> Task.CompletedTask))
// ...

话虽如此，我想知道为什么下面的代码不能编译：

let subscribeAsync (channel: IModel) exchange callback =
let consumer = AsyncEventingBasicConsumer(channel)
consumer.Received.AddHandler(AsyncEventHandler<BasicDeliverEventArgs>(fun sender args -> Task.CompletedTask))
// ...

因为我得到以下错误：

Program.fs(10, 14): [FS1091] The event 'Received' has a non-standard type. If this event is declared in another CLI language, you may need to access this event using the explicit add_Received and remove_Received methods for the event. If this event is declared in F#, make the type of the event an instantiation of either 'IDelegateEvent<_>' or 'IEvent<_,_>'.

我查看了官方的MS文档，但我看不到任何关于F#的标准事件类型的参考。

Answer 1

F#将把.NET事件公开为IEvent或IDelegateEvent类型的值，具体取决于事件声明和委托类型。只能对具有一些基本公共结构的事件执行此操作-当F#无法执行此操作时，它会将事件的底层add和remove操作公开为可以直接调用的方法。

我不太确定什么是"标准事件类型"的规则。然而，您可以从F#编译器源代码的相关部分得到一些提示：

let TryDestStandardDelegateType (infoReader: InfoReader) m ad delTy =
let g = infoReader.g
let (SigOfFunctionForDelegate(_, compiledViewOfDelArgTys, delRetTy, _)) =
GetSigOfFunctionForDelegate infoReader delTy m ad
match compiledViewOfDelArgTys with 
| senderTy :: argTys when (isObjTy g senderTy) && 
not (List.exists (isByrefTy g) argTys)  -> Some(mkRefTupledTy g argTys, delRetTy)
| _ -> None

因此，我的猜测是，"stadnard事件类型"需要：

• 至少有一个参数
• 第一个参数的类型必须为object
• 没有byref参数